feat: initial Prometheus analyzers (#855)

* feat: initial Prometheus analyzers

Added a prometheus integration with two analyzers:
1. PrometheusConfigValidate
2. PrometheusConfigRelabelReport

The integration does not deploy any Prometheus stack in the cluster.
Instead, it searches the provided --namespace for a Prometheus
configuration, stored in a ConfigMap or Secret. If it finds one, it
unmarshals it into memory and runs the analyzers on it.

PrometheusConfigValidate checks if the actual Prometheus configuration is valid or has
any errors.

PrometheusConfigRelabelReport tries to distill the scrape config
relabeling rules to give a concise label set per job that targets need
to have to be scraped. This analyzer is unconventional, in that it does
not necessarily mean there are issues with the config. It merely tries
to give a human-readable explanation of the relabel rules it discovers,
leaning on the LLM and prompt.

Tested on both kube-prometheus and Google Managed Prometheus
stacks.

Signed-off-by: Daniel Clark <danielclark@google.com>

* review: feedback cycle 1

Simplify ConfigValidate prompt and add comments.

Signed-off-by: Daniel Clark <danielclark@google.com>

* review: feedback cycle 2

Add Prometheus configuration discovery to integration activate command.

Also improve logging to make this more clear to users.

Signed-off-by: Daniel Clark <danielclark@google.com>

---------

Signed-off-by: Daniel Clark <danielclark@google.com>

pkg/integration/prometheus/prometheus.go

@@ -0,0 +1,105 @@
+package prometheus
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"os"
+
+	"github.com/fatih/color"
+	"github.com/k8sgpt-ai/k8sgpt/pkg/common"
+	"github.com/k8sgpt-ai/k8sgpt/pkg/kubernetes"
+	"github.com/spf13/viper"
+)
+
+const (
+	ConfigValidate = "PrometheusConfigValidate"
+	ConfigRelabel  = "PrometheusConfigRelabelReport"
+)
+
+type Prometheus struct {
+}
+
+func NewPrometheus() *Prometheus {
+	return &Prometheus{}
+}
+
+func (p *Prometheus) Deploy(namespace string) error {
+	// no-op
+	color.Green("Activating prometheus integration...")
+	// TODO(pintohutch): add timeout or inherit an upstream context
+	// for better signal management.
+	ctx := context.Background()
+	kubecontext := viper.GetString("kubecontext")
+	kubeconfig := viper.GetString("kubeconfig")
+	client, err := kubernetes.NewClient(kubecontext, kubeconfig)
+	if err != nil {
+		color.Red("Error initialising kubernetes client: %v", err)
+		os.Exit(1)
+	}
+
+	// We just care about existing deployments.
+	// Try and find Prometheus configurations in the cluster using the provided namespace.
+	//
+	// Note: We could cache this state and inject it into the various analyzers
+	// to save additional parsing later.
+	// However, the state of the cluster can change from activation to analysis,
+	// so we would want to run this again on each analyze call anyway.
+	//
+	// One consequence of this is one can run `activate` in one namespace
+	// and run `analyze` in another, without issues, as long as Prometheus
+	// is found in both.
+	// We accept this as a trade-off for the time-being to avoid having the tool
+	// manage Prometheus on the behalf of users.
+	podConfigs, err := findPrometheusPodConfigs(ctx, client.GetClient(), namespace)
+	if err != nil {
+		color.Red("Error discovering Prometheus worklads: %v", err)
+		os.Exit(1)
+	}
+	if len(podConfigs) == 0 {
+		color.Yellow(fmt.Sprintf(`Prometheus installation not found in namespace: %s.
+		Please ensure Prometheus is deployed to analyze.`, namespace))
+		return errors.New("no prometheus installation found")
+	}
+	// Prime state of the analyzer so
+	color.Green("Found existing installation")
+	return nil
+}
+
+func (p *Prometheus) UnDeploy(_ string) error {
+	// no-op
+	// We just care about existing deployments.
+	color.Yellow("Integration will leave Prometheus resources deployed. This is an effective no-op in the cluster.")
+	return nil
+}
+
+func (p *Prometheus) AddAnalyzer(mergedMap *map[string]common.IAnalyzer) {
+	(*mergedMap)[ConfigValidate] = &ConfigAnalyzer{}
+	(*mergedMap)[ConfigRelabel] = &RelabelAnalyzer{}
+}
+
+func (p *Prometheus) GetAnalyzerName() []string {
+	return []string{ConfigValidate, ConfigRelabel}
+}
+
+func (p *Prometheus) GetNamespace() (string, error) {
+	return "", nil
+}
+
+func (p *Prometheus) OwnsAnalyzer(analyzer string) bool {
+	return (analyzer == ConfigValidate) || (analyzer == ConfigRelabel)
+}
+
+func (t *Prometheus) IsActivate() bool {
+	activeFilters := viper.GetStringSlice("active_filters")
+
+	for _, filter := range t.GetAnalyzerName() {
+		for _, af := range activeFilters {
+			if af == filter {
+				return true
+			}
+		}
+	}
+
+	return false
+}